The Pokémon games started on the Game Boy, which had a few limitations when it came to how much data you could put on them. Technology evolves and Pokémon are all about evolving, so naturally they changed with the times, finding new ways to enhance the experience without changing the core gameplay that fans expect from the main series. In this recent video from New Frame Plus, host Daniel Floyd goes over the many additions to the battle animations as you the trainer take on other trainers through the years, while speculating what the upcoming Sword and Shield games may attempt to do.
Here’s that link to Nintendo Unity to be fair to their part in the video and to the New Frame Plus channel to see more game animation analysis. And here’s a link to JoCat’s design video also mentioned in this video. I also recommend Dr. Crafty’s videos on making Pokémon as he designed his original Pokémon. Unfortunately you’ll have to go through them because he doesn’t have a dedicated playlist as of this writing.